1. Field of the Invention
This invention relates to foamable polysiloxane compositions of the room temperature curable type which are improved in the degree of foaming and foam stability.
2. Description of the Prior Art
As set out in Japanese Patent Publication No. 45-12675, several ways of producing silicone rubber foamed articles at room temperature are known including a method wherein foaming agents are added when room temperature vulcanizable silicone rubber elastomers are obtained, and a method wherein room temperature vulcanizable silicone rubber compositions undergo foaming when cured or vulcanized. The latter method makes use of the dehydrogenation reaction between organosilicon compounds having the hydrogen atom directly joined to the silicon atom and organosilicon compounds having the hydroxyl group directly joined to the silicon atom. A number of catalysts for promoting the dehydrogenation reaction are known in the art. For instance, Japanese Patent Publication Nos. 33-9297 and 44-8755 describe quaternary ammonium salts, carboxylates of heavy metals and alkali metal alkoxides for use as the catalyst for the dehydrogenation reaction, and Japanese Patent Publication No. 45-9794 sets forth hydroxyamine compounds and organosilicon compounds having an aminoxy group directly bonded to the silicon atom. In addition, platinum compounds are taught in Japanese Laid-open Patent Application No. 51-46352.
However, the prior art foaming techniques are usually low in the degree of foaming and poor in the foam stability, thus presenting the problem on the improvement in heat insulation efficiency. Where the degree of foaming is improved by the use of .alpha., .omega.-dihydroxyorganopolysiloxane with a low degree of polymerization as set forth in Japanese Laid-open Patent Application No. 59-45330, a disadvantage is inevitably involved in that the silicone rubber foamed material has a low tensile strength.